Apparatus and method for providing power saving during idle to connected mode transitions

ABSTRACT

A method of saving power in a user device that is operable in a discontinuous reception mode, the user device comprising a receiver circuitry. The method comprises the steps of powering down at least a part of the receiver circuitry during one or more predefined power down periods during a transition between an idle mode of operation and a connected mode of operation.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/784,338 filed Apr. 4, 2014, which was the National Stage ofInternational Application No. PCT/SE2014/050419, filed Apr. 4, 2014,which claims the benefit of U.S. Application No. 61/811,922 filed onApr. 15, 2013 the disclosures of which are incorporated herein byreference in their entireties.

TECHNICAL FIELD

The present invention relates to an apparatus and method for providingdiscontinuous reception mode communication, and in particular to anapparatus and method for saving power in a user device that is operablein a discontinuous reception mode.

BACKGROUND

Communication using cellular networks has traditionally been used formobile phone applications for voice communication, and more recentlyapplications that allow smartphones, tablets, computers and the like tohandle data communications, such as Internet browsing and so forth.

A currently popular vision of the future development of communicationusing cellular networks is the possibility of having huge numbers ofsmall autonomous devices which typically transmit and receive only smallamounts of data infrequently (for example once per week to once perminute), or which are polled for data. These devices are assumed not tobe associated with humans, but are rather sensors or actuators ofdifferent kinds, which communicate with application servers thatconfigure the devices and receive data from them, within or outside thecellular network. Hence, this type of communication is often referred toas machine-to-machine (M2M) communication, and the devices may bedenoted machine devices (MDs). In the Third Generation PartnershipProject (3GPP) standardization, the corresponding alternative terms aremachine type communication (MTC) and machine type communication devices(MTC devices), with the latter being a subset of the more general termuser equipment (UE).

Due to the nature of MTC devices and their assumed typical applications,it follows that they will often have to be very energy efficient, sinceexternal power supplies will often not be available, and since it isneither practically nor economically feasible to frequently replace orrecharge their batteries. In some scenarios the MTC devices may not evenbe battery powered, but may instead rely on energy harvesting, i.e.gathering energy from the environment, opportunistically utilizing (theoften very limited) energy that may be tapped from sunlight, temperaturegradients, vibrations, and so on.

For such energy deprived devices whose traffic is characterized by smalland infrequent transactions (often delay tolerant), it is important tominimize their energy consumption.

During the time periods between communication events the devices consumeenergy, for example by keeping the radio receiver active to monitortransmissions from the cellular network. Since the periods between thecommunication events are far longer than the actual communicationevents, this energy consumption represents a significant part of theoverall energy consumption, and may even dominate the energy consumptionin scenarios where the communication events are very infrequent.

During the communication events the actual uplink (UL) transmissionsnaturally consume significant amounts of energy. This is magnified bythe large control signalling overhead that may be associated with acommunication event.

A mechanism that has been introduced in cellular networks in order tosave energy in user equipment devices, for example between communicationevents, is the discontinuous reception (DRX) mode of operation. Thediscontinuous reception mode allows a user equipment device to remain inan energy-saving sleep state most of the time, while waking up to listenfor pages in idle mode DRX, or downlink resource assignments (i.e.downlink transmissions) in connected mode DRX.

FIG. 1a shows the idle and connected modes of a communication system,for example the RCC_IDLE and RCC_CONNECTED states of the Radio ResourceControl (RRC) connection states, or the EMM-IDLE and EMM-CONNECTEDstates of the Evolved Packet System (EPS) Mobility Management (EMM)connection states. During the RRC_IDLE or EMM-IDLE states a user devicelistens to paging messages (at rare occasions) and is otherwise in a DRXsleep mode, i.e. energy saving mode. During the RCC_CONNECTED orEMM-CONNECTED states the user device is known on a cell level, but doesnot necessarily have an uplink grant or a downlink assignment. The userdevice may have DRX settings that are specific to that user device. FIG.1b shows how various timers, such as inactivity timers, on-durationtimers, retransmission timers, are used during DRX cycles in anRRC_CONNECTED state.

In order to make DRX mechanisms even more effective for energy deprivedMTC devices, 3GPP is working on extending the maximum DRX cycle length,and thus the sleep period, both for idle mode DRX and connected modeDRX. Therefore, a DRX cycle essentially consists of a sleep periodfollowed by an active period and this cycle is repeated over and overagain until the device is detached from the network. Typically, but notnecessarily, the sleep period is longer than the active period. A DRXcycle may have a more complex structure than described above, but forthe purpose of this patent application, the simplified DRX cycledescription suffices.

The idle mode DRX cycle, i.e. the paging cycle, is configured in theuser equipment device through parameters in the system information (SI)that is broadcast in each cell, in conjunction with UE specificparameters in the form of International Mobile Subscriber Identity,IMSI, modulo 1024 and an optional UE specific DRX cycle length.Alternatively, it is also possible to configure a UE specific pagingcycle. The connected mode DRX cycle and other DRX parameters (when used)are configured in the UE through optional parameters typically in aRRCConnectionReconfiguration message, during the idle to connected modetransition or later during the connected mode.

Although DRX provides power saving capabilities, UE or MTC deviceshaving communication events which are short and often infrequent sufferfrom the disadvantage that power consumption is still a problem,especially since an infrequently communicating MTC device (or other UE)will go through a transition from an idle mode to a connected mode priorto every communication event. FIG. 2 illustrates the extensivesignalling procedure involved during a typical transition from an idlemode to a connected mode (further details of which will be describedlater). This signalling during a transition from one mode to another cancontribute a significant factor to the overall energy consumption ofsuch devices.

SUMMARY

It is an aim of the present invention to provide a method and apparatuswhich obviate or reduce at least one or more of the disadvantagesmentioned above.

According to a first aspect of the present invention there is provided amethod of saving power in a user device that is operable in adiscontinuous reception mode, the user device comprising a receivercircuitry. The method comprises the steps of powering down at least apart of the receiver circuitry during one or more predefined power downperiods during a transition between an idle mode of operation and aconnected mode of operation.

According to another aspect of the present invention there is provided auser device that is operable in a discontinuous reception mode. The userdevice comprises receiver circuitry and a processing unit. Theprocessing unit is adapted to power down at least a part of the receivercircuitry during one or more predefined power down periods during atransition between an idle mode of operation and a connected mode ofoperation of the user device.

According to another aspect there is provided a method in a control nodeof a communication system, the communication system comprising one ormore user devices that are operable in a discontinuous mode ofoperation. The method comprises the steps of determining a systeminformation parameter relating to a processing event performed in thecontrol node, and transmitting the system information parameter to theone or more user devices, for use by one or more user devices forpowering down at least a part of their respective receiver circuitryduring a transition between an idle mode of operation and a connectedmode of operation.

According to another aspect, there is provided a control node of acommunication system, the communication system comprising one or moreuser devices that are operable in a discontinuous mode of operation. Thecontrol node comprises a processing unit adapted to determine a systeminformation parameter relating to a processing event performed in thecontrol node. The control node also comprises a transmitting unitadapted to transmit the system information parameter to the one or moreuser devices, for use by one or more user devices for powering down atleast a part of their respective receiver circuitry during a transitionbetween an idle mode of operation and a connected mode of operation.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example only, to the following drawings in which:

FIG. 1a shows the idle and connected modes of a communication system;

FIG. 1b shows an example of a discontinuous reception (DRX) mode of aconnected state of a communication system;

FIG. 2 (comprising FIGS. 2a and 2b ) shows a typical signalling diagramduring a transition from an idle mode to a connected mode;

FIG. 3 shows a method according to an embodiment of the presentinvention;

FIG. 4 shows an apparatus according to an embodiment of the presentinvention;

FIG. 5 (comprising FIGS. 5a and 5b ) shows an example of a signallingdiagram during a transition from an idle mode to a connected mode, andhow embodiments of the invention may be used with such a signallingdiagram;

FIG. 6 shows a method according to another embodiment of the invention;

FIG. 7 shows a method according to another embodiment of the invention;

FIG. 8 shows a method according to another embodiment of the invention;

FIG. 9 shows a method according to another embodiment of the invention;

FIG. 10 shows a method according to another embodiment of the invention;

FIG. 11 shows a method according to another embodiment of the invention;

FIG. 12 shows a method according to another embodiment of the invention;

FIG. 13 shows a method according to another embodiment of the invention;

FIG. 14 shows a method performed in a control node according to anotherembodiment of the invention; and

FIG. 15 shows a control node according to another embodiment of theinvention.

DETAILED DESCRIPTION

The embodiments of the invention will be described below in the contextof a Long Term Evolution Evolved Packet System (LTE-EPS). It is noted,however, that the invention is also intended to be applicable to otherwireless technologies, such as Universal Mobile TelecommunicationsSystem (UMTS), Wideband Code Division Multiple Access (WCDMA) and HighSpeed Packet Access (HSPA) systems.

It is also noted that references herein to a user device are intended toembrace any form of user device, including but not limited to a userequipment device (UE), a machine device (MD) or a machine typecommunication (MTC) device.

The inventors have realised that, although discontinuous reception mode(DRX) can provide power saving capabilities for communication systems,user devices having communication events which are short and ofteninfrequent still suffer from the disadvantage that the signalling thattakes place during a transition from one mode to another, (for examplefrom a Radio Resource Control (RRC) idle mode to an RRC connected mode,or from an EPS Mobility Management (EMM) idle mode to an EMM connectedmode (or ECM-IDLE mode to ECM-CONNECTED mode), can contribute asignificant factor to the overall energy consumption of such devices.

In the embodiments described below, references to a transition betweenan idle mode and a connected mode, are intended to include any of theexamples described in the preceding paragraph, relating to RRC or EMMapplications, or indeed between an idle mode and a connected mode ofsome other communication protocol.

Although the DRX mechanisms described in the background section provideenergy saving mechanisms for user equipment devices, being defined forboth idle mode and connected mode per se, i.e. when in an idle mode perse, or in a connected mode per se, there is a long period during theidle to connected mode transition phase where there are no power savingmechanisms available.

When the communication events are short and infrequent, eachcommunication event is likely to be preceded by an idle to connectedmode transition, and the transition is likely to take a significantportion of the time needed to perform the data transmission.Furthermore, the potential use of long connected mode DRX cycles alsoincreases the risk of radio link failure during mobility between cells,which means that an idle to connected mode transition will be triggeredmany times in such scenarios too.

FIG. 3 shows a method according to a first embodiment of the presentinvention. The method comprises the step of saving power in a userdevice that is operable in a discontinuous reception mode, wherein theuser device comprises a receiver circuitry. The method comprises thesteps of powering down at least a part of the receiver circuitry duringone or more predefined power down periods during a transition between anidle mode of operation and a connected mode of operation, step 301.

This has the advantage of allowing at least part of a receiver circuitryto be powered down during this transition phase from an idle mode to aconnected mode. Powering down part or whole of the receiver circuitry(or circuitry associated therewith) is particularly advantageous inmachine-to-machine type applications where communication events tend tobe few and far between.

This is because the connection setup procedure typically involves theexchange of a large number of signalling messages, such that the controlplane communication is likely to dominate over the user planecommunication. In other words, the control plane communication is likelyto comprise more messages, larger data volumes and consume more energy,than the user plane communication. Furthermore, since the signallingprocedure involves many nodes in the network as well as significantprocessing in the network nodes, e.g. in order to set the appropriateconfiguration parameters, the time intervals separating the messages maybe significant. Hence, the embodiments of the invention avoid the needfor a user device such as an MTC device (or other UE device) to activelylisten for downlink transmissions during the entire idle to connectedmode transition.

Therefore, embodiments of the invention allow energy consumption to besaved during the transition from idle mode to connected mode, thushaving a positive impact on the battery lifetime of a user device, whichis particularly advantageous in energy deprived user devices.

FIG. 4 shows a user device 40 according to another embodiment of thepresent invention, the user device 40 being operable in a discontinuousreception mode. The user device 40 comprises receiver circuitry 41 and aprocessing unit 43. The processing unit 43 is adapted to power down atleast a part of the receiver circuitry during one or more predefinedpower down periods during a transition between an idle mode of operationand a connected mode of operation of the user device 40.

According to one embodiment, the one or more predefined power downperiods are triggered by a downlink message received by the user device,and/or an uplink message transmitted from the user device, during thetransition between the idle mode of operation and the connected mode ofoperation.

This has the advantage of a predefined power down period being triggeredfrom a known type of message (or messages), such that each type ofmessage can have an associated power down period.

For example, FIG. 5 shows an example of a typical signalling sequencebetween a transition from an idle mode of operation to a connected modeof operation (similar to that shown in FIG. 2), but also shows examplesof some of the one or more predefined power down periods 51 to 57 thatcan be used to save power consumption in a user device during thetransition from an idle to a connected mode. Further details of each ofthe power down periods 51 to 57 will be provided with reference to FIGS.6 to 13 below. For simplicity it is noted that only some examples areshown in FIG. 5, and that other predefined power down periods may alsobe provided, for example in relation to other messages being receivedby, or transmitted from the user device (or in relation to a processingtask being carried out by the user device, or another device or node).It is also noted that whilst FIG. 5 shows one example of the signallingmessages that may exist during a transition from an idle mode ofoperation to a connected mode of operation, the signalling messagesduring this transitional phase may comprise a different set ofsignalling messages, for example having fewer signalling messages thanthose shown in FIG. 5, or having a greater number of signalling messagesthan those shown in FIG. 5, or having one or more different signallingmessages. As such, according to one example the transition from idlemode to connected mode may comprise a period during which signallingmessages corresponding to messages 1 to 21 of FIG. 5 exist, whileanother example may comprise a transition period during which signallingmessages corresponding to messages 1 to 4 of FIG. 5 exist. Any of thesesignalling messages may be used alone, or in combination, to trigger orhelp determine when a power down period should exist.

According to one embodiment the method comprises the steps of receivinga downlink message during the transition from the idle mode of operationto the connected mode of operation, and powering down at least a part ofthe receiver circuitry during a period when the user device isprocessing the received downlink message.

This has the advantage of powering down part or whole of the receivercircuitry when a received message is being processed by the user device,during which time the user device is not expecting another downlinkmessage.

According to another embodiment, the method comprises the steps ofreceiving a downlink message during the transition from the idle mode ofoperation to the connected mode of operation, and powering down at leasta part of the receiver circuitry during a period when the user device ispreparing a future uplink message and/or waiting for an uplinktransmission resource to be available.

This has the advantage of powering down a part or whole of the receivercircuitry while the user device is preparing a future uplink messageand/or waiting for an uplink resource to become available. This powerdown period may be combined with the power down period described above,such that the user device powers down part or whole of the receivercircuitry while processing a received downlink message, preparing thenext uplink message and/or waiting for uplink resources to becomeavailable.

According to another embodiment the method may further comprise thesteps of transmitting an uplink message during the transition from theidle mode of operation to the connected mode of operation, and poweringdown at least a part of the receiver circuitry during transmission ofthe uplink message.

This has the advantage of powering down a part or whole of the receivercircuitry while the user device is transmitting an uplink message (andhence not listening for a downlink message). It is noted that thispredefined power down period may be combined with any one or more of theother predefined power down periods described above. For example, thispredefined power down period may be combined such that the user devicepowers down part or whole of the receiver circuitry while processing areceived downlink message, preparing the next uplink message, waitingfor uplink resources to become available, and/or while transmitting theuplink message from the user device.

According to another embodiment a predefined power down period maycomprise a period when another device is processing an uplink messagewhich has been transmitted from the user device.

This has the advantage of powering down a part or whole of the receivercircuitry while another node or device is processing the uplink messagewhich has just been transmitted from the user device. This takesadvantage of the fact that the user device does not expect to receive adownlink message until the other node or device has processed the uplinkmessage which has just been sent. It is noted that this predefined powerdown period may be combined with any one or more of the other predefinedpower down periods described above. For example, this predefined powerdown period may be combined such that the user device powers down partor whole of the receiver circuitry while processing a received downlinkmessage, preparing the next uplink message, waiting for uplink resourcesto become available, while transmitting the uplink message from the userdevice, and/or while another device is processing a transmitted message.

FIGS. 6 to 11 describe examples of embodiments whereby a part or wholeof a receiver circuitry is powered down after downlink reception, beforeuplink transmission, while the user device is processing the receiveddownlink and/or future uplink data and while it is waiting for uplinktransmission resources to occur.

Referring to FIG. 6 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 52 shown in FIG. 5. The user device 40receives a message, for example a random access Response message (RAMsg2), step 601. In step 603 the user device turns off the receivercircuitry of the user device. It is noted that this may involve poweringdown a part or the whole receiver circuitry, or circuitry associatedwith the receiver circuitry. In step 605 a processing unit of the userdevice determines whether a subsequent message has been prepared, forexample whether a RRCConnectionRequest message (RA Msg3) has beenprepared, and if so turns on the receiver circuitry, step 607. As such,according to this example the receiver circuitry is powered down whilethe user device is processing the random access Response message (RAMsg2) and until the user device has prepared a RRCConnectionRequestmessage (RA Msg3). This power down period therefore includes the timeperiod for processing the received random access Response message (e.g.RA Msg2) and preparing the subsequent uplink message (e.g. RA Msg3).

Referring to FIG. 7 in combination with FIG. 5, this also describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 52 shown in FIG. 5. The user device 40receives a message, for example a random access Response message (RAMsg2), step 701. In step 703 the user device powers down the receivercircuitry of the user device. It is noted that this may involve poweringdown or turning off a part or the whole receiver circuitry, or circuitryassociated with the receiver circuitry. In step 705 a processing unit ofthe user device determines whether a subsequent uplink message, forexample a RRCConnectionRequest message (RA Msg3) has been prepared. Instep 706 it is determined whether the allocated uplink transmissionresources are ready or available for the subsequent uplink message, andif so the receiver circuitry is turned on, step 707. As such, accordingto this example the receiver circuitry is powered down while the userdevice is processing the random access Response message (RA Msg2) anduntil the uplink resources are ready or available. This power downperiod therefore includes the time period for processing the receivedmessage (e.g. RA Msg2), preparing the subsequent uplink message (e.g. RAMsg3) and waiting for the allocated uplink transmission resources to beready or occur.

According to another embodiment (not shown in a specific flow chart),the time period 52 of FIG. 5 can be similar to that described above forFIG. 7, but also include the time period for transmitting the uplinkmessage, e.g. the RA Msg3 message.

Referring to FIG. 8 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 54 shown in FIG. 5. The user device 40receives a message, for example a RRCConnectionSetup (RA Msg4) message,step 801. In step 803 the user device powers down the receiver circuitryof the user device. It is noted that this may involve powering down apart or the whole receiver circuitry, or circuitry associated with thereceiver circuitry. In step 805 a processing unit of the user devicedetermines whether a subsequent uplink message, for example aRRCConnectionSetupComplete message has been prepared, and if so turns onthe receiver circuitry, step 807. As such, according to this example thereceiver circuitry is powered down while the user device is processingthe received RRCConnectionSetup message and until the user device hasprepared the subsequent RRCConnectionSetupComplete message.

According to another embodiment (not shown in a specific flow chart),the time period 54 of FIG. 5 can be similar to that described above forFIG. 8, but also include a time period until the user device sends ascheduling request to get uplink resources to transmit theRRCConnectionSetupComplete message, and/or the time period waiting foran uplink resource to become ready or available, and/or the time periodfor transmitting the RRCConnectionSetupComplete message. The minimumtime period between the transmission of a scheduling request to anEvolved NodeB (eNB) and a consequently triggered uplink grant on thePDCCH is limited by the processing time required in the eNB forprocessing the scheduling request and performing the scheduling ofuplink transmission resources.

Referring to FIG. 9 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 55 shown in FIG. 5. The user device 40receives a message, for example a DLInformationTransfer message, step901. In step 903 the user device powers down the receiver circuitry ofthe user device. It is noted that this may involve powering down a partor the whole receiver circuitry, or circuitry associated with thereceiver circuitry. In step 905 a processing unit of the user devicedetermines whether a ULInformationTransfer message has been prepared,and if so turns on the receiver circuitry, step 907. As such, accordingto this example the receiver circuitry is powered down while the userdevice is processing the DLInformationTransfer message and until theuser device has prepared the ULInformationTransfer message.

According to another embodiment (not shown in a specific flow chart),the time period 55 of FIG. 5 can be similar to that described above forFIG. 9, but also include a time period corresponding to when the userdevice triggers a scheduling request to get uplink resources to transmitthis message, and/or the time period waiting for an uplink resource tobecome ready, and/or the time period for transmitting theULInformationTransfer message.

Thus, these embodiments provide power down periods while processing anyof the optional DLInformationTransfer messages containing a NASsignalling message and until it builds the ULIinformationTransfermessage containing the corresponding NAS response message. This timethus includes the time for preparation of the NAS response message andthe ULInformationTransfer message until the UE triggers a schedulingrequest to get UL resources to transmit the latter message.

Referring to FIG. 10 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 56 shown in FIG. 5. The user device 40receives a message, for example a SecurityModeCommand message, step1001. In step 1003 the user device powers down the receiver circuitry ofthe user device. It is noted that this may involve powering down a partor the whole receiver circuitry, or circuitry associated with thereceiver circuitry. In step 1005 a processing unit of the user devicedetermines whether a subsequent uplink message, for example aSecurityModeComplete message has been prepared, and if so turns on thereceiver circuitry, step 1007. As such, according to this example thereceiver circuitry is powered down while the user device is processingthe received SecurityMode Command message and until the user device hasprepared the subsequent SecurityModeComplete message.

According to another embodiment (not shown in a specific flow chart),the time period 56 of FIG. 5 can be similar to that described above forFIG. 10, but also include a time period corresponding to when the userdevice triggers a scheduling request to get uplink resources to transmitthis message, and/or the time period waiting for an uplink resource tobecome ready, and/or the time period for transmitting theSecurityModeComplete message.

Referring to FIG. 11 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 57 shown in FIG. 5. The user device 40receives a message, for example an RRCConnectionReconfiguration message,step 1101. In step 1103 the user device powers down the receivercircuitry of the user device. It is noted that this may involve poweringdown a part or the whole receiver circuitry, or circuitry associatedwith the receiver circuitry. In step 1105 a processing unit of the userdevice determines whether a subsequent uplink message, for example anRRCConnectionReconfigurationComplete message has been prepared, and ifso turns on the receiver circuitry, step 1107. As such, according tothis example the receiver circuitry is powered down while the userdevice is processing the RRCConnectionReconfiguration message and untilthe user device has prepared the RRCConnectionReconfigurationCompletemessage.

According to another embodiment (not shown in a specific flow chart),the time period 57 of FIG. 5 can be similar to that described above forFIG. 11, but also include a time period until the user device sends ascheduling request to get uplink resources to transmit this message,and/or the time period waiting for an uplink resource to become ready oravailable, and/or the time period for transmitting the RRCConnectionReconfigurationComplete message.

It is noted that the embodiments of the invention are intended toembrace any one or more of the time periods mentioned above being usedas power down periods during a transition from an idle mode to aconnected mode of operation, either alone or in combination.

It is also noted that in any of the embodiments described above in FIGS.6 to 11, the power down periods can be interrupted if the user devicetriggers lower layer feedback, for example a Radio Link Control (RLC)Acknowledgement. Triggering such messages also triggers transmission ofa scheduling request which requires the user device to be monitoring thePhysical Downlink Control Channel (PDCCH) for potential uplink grants.

FIGS. 12 and 13 describe examples of embodiments whereby a part or wholeof a receiver circuitry is powered down during and/or after an uplinktransmission, for a duration during which it is unlikely that anydownlink transmissions will be received from another node such as anEvolved NodeB (eNB).

According to these embodiments a user device may power down part or allof its receiver circuitry for short periods after uplink transmission(either in combination with one of the other power down periodsdescribed herein, or in isolation). The timing of these options candepend on the behaviour of another node, for example the control node,eNB, and specified communication protocols, such as LTE procedures,which is in contrast to some of the embodiments described above, wherebythe power down periods depend on criteria local or within the userequipment device itself.

Although the examples are described for an LTE Frequency Division Duplex(FDD) configuration, a similar approach is possible for Time DivisionDuplex (TDD) as well with time values modified to best suit the chosenTDD configuration, or indeed any other form of communication protocol.

Referring to FIG. 12 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 51 shown in FIG. 5. In step 1201 the userdevice transmits a message, for example a preamble message (e.g. RAMsg1). In step 1203 the user device powers down the receiver circuitryof the user device. It is noted that this may involve powering down apart or the whole receiver circuitry, or circuitry associated with thereceiver circuitry. In step 1205 a processing unit of the user devicedetermines whether a predefined period has elapsed, and if so turns onthe receiver circuitry, step 1207.

After sending the message, for example Msg1, the user device powers downpart or whole of the receiver circuitry corresponding to an expectedprocessing time of another node (or nodes), for example an eNB, which isprocessing the message which has been transmitted from the user device.For example, the random access Response window starts at the subframethat contains the end of the preamble transmission plus three subframes.This means there are at least three subframes after the one where theuser device sends Msg1 during which the user device may keep itsreceiver circuitry powered down, and without missing the subsequentResponse message (e.g. RA Msg2).

Referring to FIG. 13 in combination with FIG. 5, this describes anexample of how a part or whole of a receiver circuitry may be powereddown during a time period 53 shown in FIG. 5. In step 1301 the userdevice transmits a message, for example an RRCConnectionRequest message(RA Msg3). In step 1303 the user device turns off the receiver circuitryof the user device. It is noted that this may involve powering down apart or the whole receiver circuitry, or circuitry associated with thereceiver circuitry. In step 1305 a processing unit of the user devicedetermines whether a predefined period has elapsed, and if so turns onthe receiver circuitry, step 1307.

Thus, in this example, after sending Msg3, the user device powers downpower to part or whole of the receiver circuitry corresponding to anexpected processing time of another node (or nodes), for example an eNB,which is processing the message which has been transmitted from the userdevice. For example, a typical expected processing time for this sectioncorresponds to about 3 ms. The period that the receiver circuitry of theuser device is powered down may be specified in order to avoid DRXsynchronization state loss.

Although FIGS. 6 to 13 show examples of where power down periods may beprovided, it is noted that the receiver circuitry may be powered downduring one or more other time periods contained in FIG. 5, or othersignalling sequences between an idle mode and a connected modetransition. For example, a user device may utilize processing times,preparation times, scheduling delays, etc. in a similar manner as in theexamples described above in conjunction with FIGS. 6 to 13, wherein theinvolved messages may be one or more of messages 11, 14, 15 and 18 inFIG. 5.

For uplink data using the synchronous Hybrid Automatic Repeat request(HARQ) mechanism, the user device may power down its receiver aftertransmission until the expected feedback and potential adaptiveretransmission grant for the same HARQ process. This allows the receivercircuitry of the user device to be powered down or switched off, forexample, over the HARQ Round Trip Time (RTT) that corresponds to 8 ms inFDD. This mechanism can be applied for one or more uplink transmissionsduring the idle to connected mode transition procedure. If the userdevice is waiting for feedback and adaptive retransmission grants forother HARQ processes as well, this can be taken into account and mayaffect the length of the possible period during which the receivercircuitry is powered down.

According to some embodiments it is also possible for a user device toassume some minimum processing time after eNB reception. If this time isshort (for example a few subframes) it is almost guaranteed the eNB willnot be able to process the message and send an answer during a powerdown period of the user device. However, if the time assumed is toolong, this may lead to the user device missing the downlink transmission(or assignment).

To avoid synchronization problems with the network due to shorterprocessing times than expected, a predetermined power down period may belimited for each of these power down opportunities. For example,different values may be used depending on the type of message beingprocessed, received and/or transmitted. According to one embodiment thevalues can be fixed in specification and can correspond to the maximumprocessing times of RRC messages. In a further embodiment, a MediumAccess Control (MAC) control element (CE) is extended to provide anindication of sleep time after which the user device should again bereachable. In one embodiment this MAC CE may be sent from the eNB to theUE and the indication of sleep time may be based on the processing timesneeded in the eNB.

It can be seen from the embodiments described above that differentpredefined power down periods can have different power down durationscorresponding to a respective downlink message, an uplink message or aprocessing task or any combination thereof.

According to one embodiment a predefined power down period is smallerthan a maximum processing delay time imposed by a radio resourcecontrol, RRC, protocol specification for a respective RRC message.

The current Radio Resource Control (RRC) protocol specification for LTE,(3GPP TS 36.331 V11.2.0 “3rd Generation Partnership Project; TechnicalSpecifications Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); Radio Resource Control (RRC); ProtocolSpecification; (Release 11)”, December 2012), contains maximumprocessing delays for the different RRC messages shown in FIG. 5, fromthe point when the user device receives the message on the physicallayer up to when the user device should be ready to receive an uplinkgrant for the reply. These times correspond to the maximum times forwhich the user device may not listen to PDCCH for grants after receivingthe RRC messages. Therefore, the one or more predefined power downperiods can be configured to be a predetermined time lower than theseperiods (because of lower protocol layer functions).

This has the advantage of setting a power-down period such that it isless than a maximum processing delay set for a particulardownlink/uplink message.

According to another embodiment, a predefined power down period isspecified by one or more time windows during which no downlinktransmissions towards the user device are expected.

According to another embodiment, a predefined power down period isdynamically controlled depending upon how long a particular processingtask is taking at the user device.

This has the advantage of allowing a part or whole of the receivercircuitry to be powered down for a period which is controlled based onrules relating to the behaviour of the user device itself, rather thanRRC configuration parameters. For example, when user device receives adownlink message and powers down the receiver circuitry while processingthis downlink message, the user device can keep the receiver circuitrypowered down for as long as it takes to process the received downlinkmessage. The power down period can therefore differ from one processingevent to another, and between one user device and another, and changedynamically depending upon how long the user device is taking to processthat particular event on a particular occasion (which may be affected bywhat else the user device is having to process).

According to one embodiment the method comprises the steps ofinterrupting a power down period in response to an internal controlsignal received from within the user device. This has the advantage ofenabling a power down period to be interrupted in response to a controlsignal received from the user device, for example in response to theuser device triggering a lower layer feedback (e.g. RLCacknowledgement).

According to one embodiment the method comprises the steps of receivinga system information parameter corresponding to a minimum processingdelay in a control node associated with the user device, and setting apower down period based on the received system information parameter.

This has the benefit of covering the possibility of having a systeminformation parameter, for example where the telecom specification ischanged to allow this, so that DRX can be improved. With such anembodiment the processing delay at another node is specified explicitly,so that the user device is able to determine how long a correspondingpower down period can be.

The system information parameter may be the same for all messages orprocessing events. Alternatively, the system information parameter maybe the same for a group of messages or processing events. Alternatively,the system information parameter may be unique to each message orprocessing event. The value of the system information parameter may bechosen from a set of values, wherein each of the values in the setcorresponds to a set of processing times or power down periods, whereineach of these processing times or power down periods is associated witha different processing event or a different message, e.g. an uplinksignalling message being used in the idle to connected mode transitionprocedure. With this principle a single system information parameter mayadvantageously be used to provide information to the user device aboutall processing times and/or all allowed power down periods that may beinvolved in an idle to connected mode transition.

According to such embodiments it is possible to introduce a new systeminformation parameter informing a user device about minimum processingtimes in a node such as an eNB. This enables the user device to use DRX,i.e. enter a DRX sleep mode, during these processing times, as proposedabove. There are multiple options for how to configure minimumprocessing times. One option is to specify one minimum processing timewhich is assumed by the eNB and the user device during all processingtimes during the transition period. This parameter could also beincluded in more comprehensive information, such as a “eNB category” or“eNB capabilities” parameter similar to currently used user equipmentcategories (for example as specified in 3GPP TS 36.306 V11.2.0, “3rdGeneration Partnership Project; Technical Specification Group RadioAccess Network; Evolved Universal Terrestrial Radio Access (E-UTRA);User Equipment (UE) radio access capabilities (Release 11)”, December2012).

According to one embodiment, one or more predefined power down periodsconstitute a power saving mode of operation, and wherein the methodcomprises the step of receiving a control signal for instructing theuser device to enter into the power saving mode of operation until theend of the transition from the idle mode of operation to the connectedmode of operation, or until further notice (for example automaticallyentering the power saving mode during the next and subsequent idle toconnected transition phases, until a further control signal is receivedto disable the power saving mode of operation).

This has the advantage, for example, of allowing the user device to beset-up in this mode for the remainder of a particular idle/connectedmode transition, or for all subsequent idle/connected mode transitionsuntil further notice. This may be set, for example, in response to a MACCE command.

It is noted that the user device 40 described in FIG. 4 above maycomprise a transmitter circuitry (or any other circuitry associated witha user device), and that the processing unit 43 can be adapted toperform any of the method steps described above in relation to thevarious embodiments of the invention.

The embodiments described above provide solutions whereby a temporarydiscontinuous reception mode behaviour is implicit for the idle toconnected mode transition procedure. By implicit behaviour it is meantthat a user device may follow simple rules, which are based on existingbehaviour of the user device and are not directly dependent on any RRCconfiguration parameters. This mechanism may be configured and providedto a user device transparently, that is, the network does not need to beaware if the user device applies these rules or not.

The manner in which a user device is configured to operate may beprovided, for example, through an Over-The-Air (OTA) UniversalSubscriber Identity Module (USIM) configuration, or based on subscriberdata in the USIM, or may be hardcoded when the user device is beingdesigned. Alternatively, according to another embodiment a user deviceis configured by an application server through a message on theapplication layer. In addition, a possible option is that a network nodesuch as an eNB configures the user device using a new DRX MAC ControlElement.

During the temporary (or implicit) power down periods described abovethe embodiments work in a similar manner to a discontinuous receptionmode mechanism, (for example as described in 3GPP TS 36.321 V11.0.0,“3rd Generation Partnership Project; Technical Specification Group RadioAccess Network; Evolved Universal Terrestrial Radio Access (E-UTRA);Medium Access Control (MAC) protocol specification (Release 11)”,September 2012), whereby the user device does not listen to or monitorthe Physical Downlink Control Channel (PDCCH) continuously but mayinstead turn its receiver circuitry and associated equipment off onpredefined occasions during the state transition procedure between idlemode and connected mode.

It is noted that, according to one embodiment, the one or morepredetermined power down periods are controlled with a new DRX MACControl Element. When the user device receives this MAC Control Element,it may go to sleep (have part or whole of its receiver circuitry powereddown) according to the above described behaviour even though the legacyDRX mechanism is not configured yet. Then, a Scheduling Request (SR)transmission in uplink (either on the PUCCH or in the form of a RandomAccess) can trigger the user device to move to an active state again.The DRX MAC Control Element (CE) may be used to trigger the user deviceto apply the above described behaviour until the next uplinktransmission or for the remainder of the idle to connected modetransition procedure, or for one or more subsequent idle/connected modetransitions. This can simply be done by concatenating the MAC CE intothe same transport block with the downlink command after which nodownlink activity is expected until the user device replies.

It is noted that a user device can also combine any one or more of thevarious power down periods described above, either after downlink oruplink transmission. This means, for example, that after receiving amessage, the UE may keep its receiver circuitry powered down for theduration of the message processing and sending of uplink data until thefirst synchronous HARQ feedback is expected. As an example, the userdevice could enable its power down mechanism after receiving Msg2 inFIG. 5, until it expects to receive feedback from uplink Msg3.

The embodiments of the invention enable further energy savings to beprovided in user devices, which is particularly advantageous in energydeprived MTC devices.

It can be seen that explicit configuration is not necessarily needed,but it is possible to introduce this, if wanted.

In some embodiments the power up of the receiver circuitry is triggeredby the start of an uplink transmission, possibly with some delay toallow time for the receiving eNB and other potentially involved networkentities (depending on the nature of the uplink transmission) to processthe uplink transmission and prepare a response.

It can be seen from the above that the inventors have realised thatsignificant power savings can be made during the transition period froman idle mode to a connected mode of operation.

FIG. 14 shows a method performed in a control node of a communicationsystem, according to another embodiment of the invention, where thecommunication system comprises one or more user devices that areoperable in a discontinuous mode of operation. The control node maycomprise any form of control node, including for example an EvolvedNodeB, eNB. The method comprises the step of determining a systeminformation parameter relating to a processing event performed in thecontrol node, step 1401. In step 1403 the system information parameteris transmitted to the one or more user devices, for use by one or moreuser devices for powering down at least a part of their respectivereceiver circuitry during a transition between an idle mode of operationand a connected mode of operation.

The system information parameter may comprise information relating to aprocessing delay associated with a processing event performed in thecontrol node, and/or a processing delay associated with processinguplink and/or downlink signalling messages relating to the transitionbetween the idle mode and the connected modes of operation, and/orprocessing delays in the user devices.

According to one embodiment the system information parameter is the samefor all messages or processing events. Alternatively, the systeminformation parameter is the same for a group of messages or processingevents. Alternatively, the system information parameter is unique toeach message or processing event.

According to one embodiment the value of the system informationparameter is chosen from a set of values, wherein each of the values inthe set corresponds to a set of minimum processing delays, wherein eachof these minimum processing delays is associated with a differentprocessing event or a different message.

According to one embodiment the method performed in the control nodecomprises the step of transmitting a control signal to one or more userdevices, the control signal instructing the user device to enter into apower saving mode of operation until the end of a transition from theidle mode of operation to the connected mode of operation, or untilfurther notice.

FIG. 15 shows a control node 1500 of a communication system, accordingto another embodiment of the present invention, wherein thecommunication system comprises one or more user devices that areoperable in a discontinuous mode of operation. The control node 1500comprises a processing unit 1501 adapted to determine a systeminformation parameter relating to a processing event performed in thecontrol node 1500. The control node 1500 comprises a transmitting unit1503 adapted to transmit the system information parameter to the one ormore user devices, for use by one or more user devices for powering downat least a part of their respective receiver circuitry during atransition between an idle mode of operation and a connected mode ofoperation.

The system information parameter may comprise information relating to aprocessing delay associated with a processing event performed in thecontrol node, and/or a processing delay associated with processinguplink and/or downlink signalling messages relating to the transitionbetween the idle mode and the connected modes of operation, and/orprocessing delays in the user devices.

According to one embodiment the processing unit 1501 is adapted togenerate a system information parameter that is the same for allmessages or processing events, or a system information parameter that isthe same for a group of messages or processing events, or a systeminformation parameter that is unique to each message or processingevent.

According to one embodiment the processing unit 1501 is adapted toselect a value of the system information parameter from a set of values,wherein each of the values in the set corresponds to a set of minimumprocessing delays, wherein each of these minimum processing delays isassociated with a different processing event or a different message.

According to one embodiment the transmitting unit 1503 is adapted totransmit a control signal to one or more user devices, the controlsignal instructing the one or more user devices to enter into a powersaving mode of operation until the end of a transition from the idlemode of operation to the connected mode of operation, or until furthernotice.

The various embodiments show how a user device may power down itsreceiver circuitry, and related functions, during certain periods duringthe idle to connected mode transition. The user device may power downits receiver completely when it is processing messages after receivingthem in downlink, and after sending uplink messages, for brief periodsof time before expected HARQ feedback or when the specifications dictatea time window during which there are no expected downlink transmissionstowards the UE.

References herein to powering down at least a part of a receivercircuitry during events such as transmission of an uplink message,processing a task, or while waiting for resources to become available,are intended to include the receiver circuitry being powered down for atleast a portion of such events, for example at least a portion of thetime period corresponding to when an uplink message is beingtransmitted, or at least a portion of the time period during whichprocessing is taking place, or at least a portion of the time periodwaiting for resources to become available.

Furthermore, references to powering down at least a part of a receivercircuit include turning off power completely to at least a part of areceiver circuit, or reducing power to at least a part of a receivercircuit, for example reducing power to a low power state, or acombination of turning off and reducing power in different parts of areceiver circuit.

It is also noted that references herein to a transition between an idlemode and a connected mode are intended to include going from an idlemode to a connected mode, and/or going from a connected mode to an idlemode.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims. The word “comprising” does not excludethe presence of elements or steps other than those listed in a claim,“a” or “an” does not exclude a plurality, and a single processor orother unit may fulfil the functions of several units recited in theclaims. Any reference signs in the claims shall not be construed so asto limit their scope.

1. A method of saving power in a user device that is operable in adiscontinuous reception mode, the user device comprising a receivercircuitry, and the method comprising the steps of: turning off power toat least a part of the receiver circuitry during one or more predefinedpower down periods during a transition between an idle mode of operationand a connected mode of operation.
 2. The method as claimed in claim 1,wherein the one or more predefined power down periods are triggered by adownlink message received by the user device, and/or an uplink messagetransmitted from the user device, during the transition between the idlemode of operation and the connected mode of operation.
 3. The method asclaimed in claim 1 or 2, wherein the method comprises the steps of:receiving a downlink message during the transition from the idle mode ofoperation to the connected mode of operation; and powering down at leasta part of the receiver circuitry during a period when the user device isprocessing the received downlink message.
 4. The method as claimed inclaim 1, wherein the method comprises the steps of: receiving a downlinkmessage during the transition from the idle mode of operation to theconnected mode of operation; and powering down at least a part of thereceiver circuitry during a period when the user device is preparing afuture uplink message and/or waiting for an uplink transmission resourceto become available.
 5. The method as claimed in claim 1, furthercomprising the steps of: transmitting an uplink message during thetransition from the idle mode of operation to the connected mode ofoperation; and powering down at least a part of the receiver circuitryduring transmission of the uplink message.
 6. The method as claimed inclaim 1, wherein a predefined power down period comprises a period whenanother device is processing an uplink message which has beentransmitted from the user device.
 7. The method as claimed in claim 1,wherein different predefined power down periods have different powerdown durations corresponding to a respective downlink message, an uplinkmessage or a processing task.
 8. The method as claimed in claim 1,wherein a predefined power down period is smaller than a maximumprocessing delay time imposed by a radio resource control (RRC) protocolspecification for a respective RRC message.
 9. The method as claimed inclaim 1, wherein a predefined power down period is specified by one ormore time windows during which no downlink transmissions towards theuser device are expected.
 10. The method as claimed in claim 1, whereina predefined power down period is dynamically controlled depending uponhow long a particular processing task is taking at the user device. 11.The method as claimed in claim 1, further comprising interrupting apower down period in response to an internal control signal receivedfrom within the user device.
 12. The method as claimed in claim 1,further comprising the steps of: receiving a system informationparameter corresponding to a minimum processing delay in a control nodeassociated with the user device; and setting a power down period basedon the received system information parameter.
 13. The method as claimedin claim 12 wherein: the system information parameter is the same forall messages or processing events; or the system information parameteris the same for a group of messages or processing events; or the systeminformation parameter is unique to each message or processing event. 14.The method as claimed in claim 12, wherein: the value of the systeminformation parameter is chosen from a set of values, wherein each ofthe values in the set corresponds to a set of minimum processing delays,wherein each of these minimum processing delays is associated with adifferent processing event or a different message.
 15. The method asclaimed in claim 1, wherein the one or more predefined power downperiods constitute a power saving mode of operation, and wherein themethod further comprises the step of receiving a control signal forinstructing the user device to enter into the power saving mode ofoperation until the end of the transition from the idle mode ofoperation to the connected mode of operation, or until further notice.16. A user device that is operable in a discontinuous reception mode,the user device comprising: receiver circuitry; and a processor; whereinthe processor is adapted to power down at least a part of the receivercircuitry during one or more predefined power down periods during atransition between an idle mode of operation and a connected mode ofoperation of the user device.
 17. The user device as claimed in claim16, wherein the user device further comprises transmitter circuitry, andwherein the one or more predefined power down periods are triggered by adownlink message received by the user device, and/or an uplink messagetransmitted from the user device, during the transition between the idlemode of operation and the connected mode of operation.
 18. The userdevice as claimed in claim 16, wherein: the receiver circuitry isadapted to receive a downlink message during the transition from theidle mode of operation to the connected mode of operation; and theprocessor is adapted to power down at least a part of the receivercircuitry during a period when the user device is processing thereceived downlink message.
 19. The user device as claimed in claim 16,wherein: the receiving circuitry is adapted to receive a downlinkmessage during the transition from the idle mode of operation to theconnected mode of operation; and the processor is adapted to power downat least a part of the receiver circuitry during a period when the userdevice is preparing a future uplink message and/or waiting for an uplinktransmission resource to become available.
 20. The user device asclaimed in claim 16 further comprising: transmitting circuitry adaptedto transmit an uplink message during the transition from the idle modeof operation to the connected mode of operation; and wherein theprocessor is adapted to power down at least a part of the receivercircuitry during transmission of the uplink message
 21. The user deviceas claimed in claim 16, wherein the processor is adapted to dynamicallycontrol a predefined power down period depending upon how long aparticular processing task is taking at the user device.
 22. (canceled)23. A control node of a communication system, the communication systemcomprising one or more user devices that are operable in a discontinuousmode of operation, the control node comprising: a processor adapted todetermine a system information parameter relating to a processing eventperformed in the control node; and a transmitter adapted to transmit thesystem information parameter to the one or more user devices, for use byone or more user devices for powering down at least a part of theirrespective receiver circuitry during a transition between an idle modeof operation and a connected mode of operation.
 24. The control node asclaimed in claim 23, wherein the system information parameter comprisesinformation relating to a processing delay associated with a processingevent performed in the control node, and/or a processing delayassociated with processing uplink and/or downlink signalling messagesrelating to the transition between the idle mode and the connected modesof operation, and/or processing delays in an user device.
 25. Thecontrol node as claimed in claim 23, wherein the processor is adapted togenerate a system information parameter that is the same for allmessages or processing events, or a system information parameter that isthe same for a group of messages or processing events, or a systeminformation parameter that is unique to each message or processingevent.